Why is moisture forming on or in my window?

It depends on where the condensation is forming:

Inside your window – When condensation forms between panes of glass in an insulated glass unit, the seals have most likely failed and the glass might need to be replaced. We can help you determine if replacement can be covered under the manufacturer’s warranty, and are happy to stop by and give you a free quote for replacing your window.

On the window exterior  – Exterior condensation results from dew, and since the window glass is usually slightly cooler than other materials around it, dew forms on that surface first.  In fact, exterior moisture can demonstrate that your windows are working properly and retaining heat inside your house.

On the window interior – This often means that your windows are preventing air leakage. For the best explanation on why interior condensation forms and how to minimize it, check out this video by Anderson:

Interior condensation may also indicate that your house has excessive humidity. Window glass is usually cooler than the rest of your room, so when warm air laden with moisture comes in contact with the glass, the moisture condenses on the glass. Signs of excessive humidity can include a damp feeling in the air, mold or mildew on surfaces, a “musty” odor, sweaty pipes, blisters in interior or exterior paint, or warped wooden surfaces.

How to prevent interior condensation – Many daily activities (such as showering, cooking, laundry and breathing) put moisture in the air, but humidity can be controlled. Simple things, like running exhaust fans during showering and cooking, cut down on moisture in the air. You can also reduce interior window condensation by leaving window coverings (like blinds) open to allow air flow, or occasionally leaving doors to closed-off rooms open for a while.